Output devices are utilized to provide a high driving ability of integrated circuits. For example, driving stages that include operational amplifiers, are used to increase the driving ability of analog circuits. However, in many situations, output devices are coupled between output pads and the integrated circuits. The output devices suffer over-stress voltage, such as electrostatic discharge (ESD) pulses, from the output pads. As a result, a permanent damage on the output devices may result, and the operations of overall devices could fail.